1. Field of the Invention
The present invention relates to the manufacture of integrated circuits and other electronic devices on substrates. More particularly, the invention relates to a method and apparatus for aligning a substrate, a shadow ring, and a pedestal within a processing chamber.
2. Background of the Related Art
In the manufacture of integrated circuits and other electronic devices, multiple layers of materials are deposited onto and etched from substrates to form interconnections between electronic devices implanted in the substrate. Processing systems typically include vacuum processing chambers in which substrates are supported on pedestals. The equipment is designed to introduce substrates into the chambers via robot assemblies and to place the substrates on the pedestal for processing.
In some processes, it has become important to prevent deposition on the edge and backside of the substrates, because such deposited material can flake off these surfaces and become particles that may compromise the integrity of a chip derived from that or other substrates. To address this challenge, shadow rings have been used to shield the outer edge of the substrate from the deposition material. One system that utilizes shadow rings is the WxZ(trademark) chamber available from Applied Materials, Inc., located in Santa Clara, Calif. The shadow ring is placed on the pedestal, adjacent the substrate edge, to shadow that edge from deposition material.
One difficulty encountered in the use of pedestals and shadow rings is that it is very difficult to align the substrate, the pedestal, and the shadow ring. Typically, the substrate is aligned to the pedestal and the shadow ring is then separately aligned to the pedestal. Thus, the substrate is indirectly aligned to the shadow ring. Depending on the system tolerances and wear of the parts, the indirect alignment may not insure sufficient shadowing of the substrate edge.
FIG. 1 shows one typical arrangement of a shadow ring positioned over a substrate in a chemical vapor deposition (CVD) chamber 2. The chamber has sidewalls 4, top wall 6, and bottom wall 8. At the top is a gas inlet 12 connected to a gas distribution element 20, such as a xe2x80x9cshowerheadxe2x80x9d, which uniformly delivers gases into the chamber. Near the chamber bottom is a pedestal 22 that may include a lift tube 24 and a pedestal lift 26. The pedestal 22 supports a substrate 28, such as a wafer, on its upper surface during processing. The substrate may be held in place on the pedestal by a plurality of vacuum passages. A set of lift pins 34 extend through channels in the pedestal to lift and place a substrate between a robot blade and the pedestal. The pins are supported on their lower end on a lift plate 36 that is raised and lowered by a pin lift shaft 38 and a lift plate lift 40. The pedestal also includes a gas conduit 42 which is in fluid communication with a gas supply 41 and delivers a purge gas through an annular gas outlet 44, typically about 0.5 to 1.0 mm wide disposed about the perimeter of the pedestal upper surface. The purge gas flows from the annular gas outlet 44 through the gap 48 (shown in FIG. 2), typically about 0.1 mm to 0.3 mm high between the shadow ring and substrate to prevent deposition gases from depositing on the substrate edge and backside. A shadow ring 30 is mounted above the pedestal.
To receive a substrate on the pedestal, the pedestal is lowered, such that the top surface of the lift pins extend through the pedestal. A robot arm (not shown) delivers a substrate to the chamber and places it on the extending pins, typically by virtue of an upward extension of the pins to lift the substrate off the robot, which also provides clearance for the robot retraction. The pedestal then raises to lift the substrate off the lift pins and into proximity to the shadow ring. Process gases flow through the gas inlet and through the showerhead and form a layer(s) on the substrate through thermal decomposition. The shadow ring shields the substrate from the process gases. In theory, the substrate is properly positioned on the pedestal, so that the substrate uniformly overhangs only a portion of the annular space 44. This position allows a non-process gas to flow around the substrate periphery and protect the periphery from the process gases. The concept is disclosed in U.S. Pat. No. 5,516,367, issued to Applied Materials, Inc., the assignee of the present invention, and is incorporated herein by reference.
One challenge presented is to provide proper positioning of the substrate 28 to the shadow ring 30. Where the substrate and shadow ring are misaligned, the gas which is introduced around the substrate edge will experience a different flow resistance about the substrate perimeter, with a resulting differential flow at different substrate edge locations. As a result, backside deposition may occur in low flow areas and the film layer formed on the substrate surface may be disturbed in the non-standard edge purge gas flow area.
Some attempts have been made to forcibly move the substrate laterally after mounting the substrate to the pedestal to better align the shadow ring and substrate by including tapered surfaces on the shadow ring. However, such movement may scrape the substrate surface and leave substances on the pedestal which may then interfere with the operation of the vacuum chuck, or allow the process gases to infiltrate the substrate backside and deposit thereon, creating further contaminants in the processing system and scrap in the process.
Other prior efforts, aimed at reducing particle creation, have reduced or eliminated lateral movement of the substrate with respect to the pedestal and simply increased the shadow ring overhang. By increasing the overhang, the shadow ring is able to overlap the substrate without substantial lateral, aligning movement of the substrate. One way that the increased overhang is accomplished is by decreasing the inner diameter of the shadow ring upper end 52, shown in FIG. 2, so that this diameter is smaller relative to the substrate diameter, resulting in a larger overhang 50. Thus, although these systems accept a greater substrate to shadow ring misalignment, the greater overhang shadows usable portions of the substrate which results in a reduction in usable processed surface area.
Current industry practice demands that at least ninety percent (90%) of film thickness required to be deposited over the entire face of the substrate be present at 3 mm from the substrate edge. However, more recent industry practices have pressed for more efficient systems having a higher film uniformity, i.e., much more than 90%, up to the 3 mm edge, and have even considered imposing film uniformity to a 1.5 mm edge, while preventing all film deposition at the substrate bevel. A substrate has beveled edges that measure 0.5 mm from the substrate edge. To comply with these requirements, the margin for error in aligning the substrate on the pedestal is preferably no greater than about 1 mm measured along the substrate radius. Therefore, prior efforts to avoid close substrate alignment and cover more surface area will not meet these more stringent requirements.
Therefore, there is a need to provide an improved method and related equipment to directly align a substrate and a shadow ring with respect to each other.
The invention generally relates to a processing system which includes a process chamber, a pedestal disposed in the process chamber, a shadow ring and an alignment and support member that receives and directly aligns a substrate with a shadow ring, independently of the pedestal.
In one aspect of the invention, a shadow ring is provided which includes an upper shielding portion and one or more lower alignment and support members. The alignment and support member preferably includes one or more alignment and support tabs. A set of lift pins are preferably disposed in the chamber to align the substrate and shadow ring with the pedestal. At least one pedestal recess may be located in the pedestal to receive the alignment and support member, and may also align the shadow ring with the pedestal in addition to, or in lieu of, the lift pins.
In another aspect of the invention, a processing chamber is provided with the shadow ring and pedestal of the invention disposed therein. In operation, a robot blade introduces a substrate into the chamber and inserts it into a shadow ring having alignment and support tabs that align and support the substrate directly in the lower portion of the shadow ring. Having aligned the shadow ring with the substrate, lift pins and/or pedestal recesses then align the shadow ring supporting the substrate with the pedestal as the substrate is received onto the pedestal. The present invention may also include a method of aligning a substrate shield and a substrate over a pedestal, including introducing a substrate into a chamber between a substrate shield and a substrate alignment and support member connected to the substrate shield, receiving the substrate into the alignment and support member, and moving the substrate and the alignment and support member onto the pedestal.